210
CHEMICAL ENGINEERING
Then
Ax = Weight of finished size in original feed, By = Weight of finished size in classifier sands, C(x — y) = Weight of finished size in mill discharge, and Dx = Weight of finished size in classifier overflow.
As before, the .weight of finished size in the material going to the classifier will equal the weight of finished size in the classifier products, so
or
C(x + y) = By + Dx
__ (D -C)
y' - (C - B) *
The ratio of circulating load (R) to original feed would be
A ~ ~T~ " ^ lc ~ x ^ (C - B)
Example 4.—As an illustration, suppose the figures are the same as in Example (1) except the percentage of undersize in the tube-mill discharge.
—65 mesh in the original feed......
—65 mesh in the classifier sands
-65 mesh in the mill discharge.....
—65 mesh in the classifier overflow. Substituting in the equation, R = 1.87.
PER CENT 38.0 27.8 59.4 87.0
Properly speaking, the circulating load is that part of the load which circulates, or returns to the starting point. In the case of the feed going direct to the ball mill, the circulating load is made up of the classifier sands only, as that is the only part of the original feed which completes the cycle. Following this concept, the ratio (R)
Y Y
of circulating load to original feed would be R - — instead of 1-----.
x x
HORSEPOWER REQUIRED PER FOOT OF MILL LENGTH
Internal Proportion of mill volume occupied by charge
diameter
of mill,
feet 0.1 0.2 0.3 0.4 0.5 0.6
1 0.0023 0.0099 0.022 0.042 0.065 0.093
2 0.0255 0.1100 0.254 0.460 0.730 1.040
3 0.1087 0.4630 1.070 1.940 3.070 4.380
4 0.288 1.2400 2.870 5.220 8.250 11.780
5 0.640 2.7200 6.290 11.430 18.070 25 . 740
6 1.200 5.1600 11.880 21.470 34.140 48.690
7 2.060 8.8500 20.430 37.060 58.610 83.530
8 3.260 14.1200 32.540 59.080 93.460 133.320
9 4,960 21.3200 49.090 89.310 141.240 201.330
10 7.130 30.8100 71.060 129.000 204.070 291.100
1
In this table the mill is assumed to be operating at the most efficient speed, as shown in the following table, and the charge is assumed to weigh 325 Ib. per cubic foot.